The present invention relates to the art of earth boring and more particularly to a rotary rock bit with means for conducting heat from the bearings between the rock bit body and a rotatable cutter mounted on the rock bit body.
A rotary rock bit, in general, consists of a main bit body adapted to be connected to a rotary drill string. The bit includes at least one rotatable cutter mounted upon a bearing shaft extending from the main bit body. Bearing systems are povided between the rotatable cutter and the bearing shaft to promote rotation of the cutter and means are provided on the outer surface of the cutter for disintegrating the earth formations as the bit and cutter are rotated.
The operating life of the bearing systems of the rock bit are frequently governed by the temperature reached at the bearing systems during drilling. High temperatures may be encountered in the borehole during the drilling operations and when this high-temperature environment is coupled with the heat generated by the rotation of the rock bit, the resulting temperature may cumulate in damage to the bearings. The temperature of the borehole will rise as the borehole penetrates deeper into the earth and temperatures in the range of 250.degree. F to 350.degree. F at 10,000 feet depth may be expected with even higher temperatures at greater depths. Deep wells now being drilled are expected to result in environmental temperatures of up to 400.degree. F and the drilling of steam wells results in environmental temperatures as high as 550.degree. F. As the bit is rotated and the rotatable cutters engage the formations, a large amount of heat is generated, causing the temperature at the bearing systems to rise.
In prior art rotary rock bits, the heat generated at the bearings would blow outward through the steel or other materials of the rock bit body or the cutter to the cooling drilling fluid being circulated through the borehole. Dissipation of heat in this way is inefficient and bearing failure due to overheating is frequent. It will, therefore, be appreciated that a need clearly exists for a rotary rock bit with means for conducting heat from the rock bit's bearings.